Explosive composition



0 30, 1962 E. M. SCOTT, JR

EXPLOSIVE COMPOSITION Filed Sept. 16, 1959 INVENTOR. EDWIN M. 5COTT JR.

2o 40 PERCENT "sN" IN "AN SN "MIXTURE AGENT 3,061,488 Patented Oct. 30, 1962 3,061,488 EXPLOSIVE COMPOSITION Edwin M. Scott, Jr., Los Angeles, Calif. (P.O. Box 323, Tujunga, Calif.) Filed Sept. 16, 1959, Ser. No. 840,453 8 Claims. (Cl. 149-5) This invention relates to explosive compositions, and more particularly to detonatable mixtures of ammonium nitrate and sodium nitrate with a hydrocarbon.

It has been known for about a century that ammonium nitrate may be detonated when mixed with a small amount of carbonaceous material. In recent years, a relatively new physical form of ammonium nitrate known as prills has become commercially available, and it has been found that this form of ammonium nitrate is particularly well-adapted to explosive uses by the simple admixture of a hydrocarbon such as diesel oil. Since the prills are not solid crystals but aggregations of microcrystals, the liquid hydrocarbon is able to be taken up by the ammonium nitrate prill and to penetrate it, furnishing a particularly intimate admixture of hydrocarbon sensitizer and ammonium nitrate. Mixtures of this sort are detonated with Various primer charges, the most common being dynamite, generally in an amount very small compared to the amount of ammonium nitrate which is detonated.

Satisfactory as the known mixtures may be, particularly in comparison to the earlier use of relatively expensive explosives such as dynamite which the ammonium nitrateoil mixture has displaced to a great extent, nevertheless the utilization of ammonium nitrate for this purpose is subject to substantial improvement.

An object of the present invention is to provide a composition based on ammonium nitrate which has greater explosive power than the ammonium nitrate compositions of the type described and heretofore known.

Another object of the invention is to provide a novel composition which permits lower cost by the inclusion of sodium nitrate, while at the same time increasing instead of decreasing the explosive effect.

Another object of the invention is to provide an armmonium nitrate type of explosive of substantially greater density than ammonium nitrate while at the same time achieving greater, rather than lesser explosive power.

Other objects of the invention will appear as the description thereof proceeds.

Generally speaking and in accordance with an illustrative embodiment of my invention, I mix together ammonium nitrate prills, free of the clay, diatomaceous earth or other mineral filler coating commonly used thereon, with sodium nitrate within a range of relative proportions by weight which I have discovered give extraordinary, unexpected and surprising results, together with a liquid hydrocarbon oil. More particularly, I may use ammonium nitrate pri'lls of the type described and ordinary sodium nitrate such as Chile nitrate, in a mixture in which the sodium nitrate is present within the range of about 15% to about 75% by weight of the total mixture of sodium nitrate and ammonium nitrate. To this mixture of the two nitrates I add a suitable quantity of a hydrocarbon, which most suitably is between 3 and parts by weight of hydrocarbon per 100 parts by weight of the nitrate mixture, but optimally about 6 parts, and for which I have found liquid hydrocarbon oils such as diesel oil to be best.

As remarked, it has been known for many years that ammonium nitrate is detonatable when sensitized with a carbonaceous material, but this not true of sodium nitrate, and sodium nitrate has always been considered, and properly so, simply as a sort of lower-performance diluent for of an inch in diameter.

ammonium nitrate when used in detonatable mixtures. The usual effects, and indeed those to be expected, from the admixture of sodium nitrate to ammonium nitrate in the commonly used forms of the latter may be seen from the following tabulation:

Table I Crater Diameters Composition of Mix Coated Coated Coated AN Stengle Grained Prills Flake AN AN 100 parts AN 5.8 parts diesel 8,0 2,0" 5,8 parts AN 30 parts Chile SN. 6'3 1'2" 5'6 5 8 parts diesel oil 70 parts AN 30 parts Arcadian SN 3'10 0 4 5.8 parts diesel oil In the above table, results are given for three different types of ammonium nitrate, alone and mixed in a 70:30 ratio with two types of sodium nitrate. The abbreviations AN, SN are used throughout this specification for ammonium nitrate and sodium nitrate respectively.

In the tests the results of which are given in Table I, 18 inch deep holes were bored in a uniform moist clay playa deposit in the Mojave Desert in Kern County, California, this particular. deposit being Widely used for explosive tests of this nature. The holes were loaded with 1500 grams of the explosive mixture and half a stick of dynamite. The holes were thoroughly backfilled and tamped, and the dynamite detonated. The crater formed by the blast was measured, and the crater diameters appear in Table 1. Experience with this deposit has shown that results are very highly reproducible, because of the uniform nature of the deposit.

It will be seen from Table I that in all cases, where sodium nitrate was admixed with ammonium nitrate in a 30:70 ratio, markedly poorer results were obtained than with the straight ammonium nitrate.

Ammonium nitrate prills, as mentioned, are a relatively recent development. Their manufacture is described in an article entitled Ammonium Nitrate in Industrial and Engineering Chemistry, volume 45, pages 496-504, March 1953. Essentially, the process consists in spraying hot concentrated ammonium nitrate solution from the top of a tower and allowing the droplets to descend against a countercurrent stream of air at a lower temperature, forming solid particles which are essentially aggregations of microcrystals, which are termed prills, about A to The basic process widely used is described in United States Patent 2,402,192. Instead of using gravity to move the droplets of ammonium nitrate solution through a tower, prilling may also be accomplished in a rotating drum, as described in Chemical and Engineering News, June 22, 1959, pages 38-39. Ammonium nitrate is subject to caking, particularly in storage, so that it is common practice to coat the prills formed in the fashion described with an anti-caking agent, which most commonly consists of 2 to 3 /2% by weight of a mineral filler powder such as diatomaceous earth, attapulgite clay, talc, ground limestone, and the like. As appears from Table I above, however, coated prills are not improved in explosive character by the admixture of sodium nitrate, but rather just the opposite. Indeed, this statement applies to the other available forms of ammonium nitrate as well, as also appears from Table I. It is an essential feature of the present invention that ammonium nitrate must be used not only in its prill form but also in the form of prills which are free of the common mineral filler coating. Accordingly, throughout this specification and the claims which follow, the term uncoated prilled ammonium nitrate it is to be understood as the prills of this substance as produced in a prilling tower or drum or by like means, and free of the usual 2 or 3 or 4% of mineral filler. I have carried out experiments with slightly coated prills, and find that the ammonium nitrate prills may have up to and including "/2% by weight, but no more, of a mineral filler coating, and still be operative in my invention. Any increase in coating over this amount greatly decreases the eificiency. Minute quantities of organic additives which are occasionally used to improve the physical properties of the prills, such as to 1% of an organic surface active agent or a wax, do not interfere with the practice of the invention. Materials of this sort are more or less soluble in the diesel or other hydrocarbon oil which is used in the practice of my invention, and combust along with the oil.

By way of further explanation of Table I and exemplary of other forms of ammonium nitrate which do not work in my invention are the so-called Stengle flake, made in accordance with Stengle Patent 2,568,901, which as the name implies is in flake form and thus wholly unlike a prill; and gained ammonium nitrate which is made by open-pan evaporation and results in granules which are considerably smaller than prills but do not have the microcrysta'lline structure of the prills. The manufacture of ammonium nitrate by graining is described in the Industrial and Engineering Chemistry article already cited, and Stengle flake in IEC 46,622632 (1954).

I have found that both of the commercially available forms of sodium nitrate work substantially equally well in my invention. These are the natural sodium nitrate from Chile known as Chile nitrate or Chi'le saltpeter, and that produced in the United States by neutralization of synthesized nitrogen oxides and known in the trade as Arcadian nitrate. Domestic sodium nitrates are usually available in crystalline or grained form (although recent- 1y a domestic variety has been made available in prilled form) whereas the Chilean sodium nitrate (which was formerly available only in coarse crystals) is now available in a so-called prilled form. They resemble ammonium nitrate prills only in their spherical form. They have a wider range of particle size and an appreciable amount is plus mesh. The sodium nitrate in all of these forms is dense and hard and shows no appreciable absorption of hydrocarbon oil. Laboratory grade, i.e., C.P. sodium nitrate of course also works very well, but is too expensive for field use.

The hydrocarbon used in the practice of my invention may be any commonly available hydrocarbon, such as petroleum, petroleum fractions, waxes, asphalts, coal tar hydrocarbons, pinewood hydrocarbons, and the like. The best I have found to be liquid or readily liquifiable hydrocarbon oils, and particularly petroleum hydrocarbon oil of the types included within the range of kerosene through light lubricating oil. In general, hydrocarbons of higher gravity than kerosene are too volatile for convenience in use, although they may still be used, while lubricating oils heavier than about SAE 10 are not only more expensive but take too long to become absorbed to equilibrium by the prills. The best hydrocarbon oil which I know of is No. 2 diesel oil which is known as class 2 diesel fuel oil in the United States Military Specifications.

A striking feature of compositions made in accordance with my invention is that the mixture of ammonium nitrate and sodium nitrate is no longer subject to the caking of the straight ammonium nitrate.

The surprising results achieved in the practice of my invention may be most readily appreciated by reference to the drawing, in which two curves are shown which show the explosive effectiveness of mixtures made in accordance with my invention as a function of the percent sodium nitrate in the mixture of the two nitrates. The figures as Table Table II Crater Diameter Relative Crater (in feet) Percent SN in AN-SN Mixture Bulk Diameter Cubed Density (in feet) Times Cubed 1 Relatii e Density 1 1.00 1,000 1,000 1. 04 729 757 1. 08 812 878 l. 10 860 949 1. 12 1,000 1, 116 1. 13 1,210 1, 356 1. 18 1, 461 l, 718 1. 23 1, 000 1, 232 1.29 1,000 1.293 1. 36 904 l, 228 1. 43 166 233 1 Plotted in drawing as dashed line. 2 Plotted in drawing as solid line.

In the tests which were made which are shown in Table II, uncoated ammonium nitrate prills were mixed in various proportions with ordinary commercial Chile sodium nitrate. The percentage of sodium nitrate in the mixture of the two nitrates appears in column 1. The second column shows the relative bulk density of the mixture of the nitrates and diesel oil, which was held constant at 5.8 parts by weight of diesel oil per parts of nitrate mixture. The third column of Table H shows the cube of the crater diameter in feet, while the fourth column shows this figure multiplied by the relative bulk density which appears in column 2.

In commercial blasting operations, such as for example the open-pit mining of coal, iron ore, and the like, an appreciable part of the cost of the blasting operation is the drilling of the holes to receive the charge. If one explosive has a lesser bulk density than another, then it will be necessary to drill a larger hole when using the first than when using the second, and in consequence the overall blasting costs will be greater for the first than for the second, even if explosive effectiveness on a weight basis and cost per unit weight Were the same for both explosives. Frequently hard, dense rock formations are encountered that require greater shattering action than the bulkier explosives can develop. It has been well established both by theory and practice that of two explosives having equal strength to weight ratio, the one having the greater density will develop the greater shattering effect or brisance. This is because the shock wave in the denser explosive will have a greater velocity providing both have the same strength to weight ratio. Heretofore efforts to increase density of ammonium nitrate type explosives have always resulted in decreasing the strength to weight ratio so that any advantage in cramming more mass into the drill hole has been virtually nullified by the decreased strength to weight ratio. This has been particularly true with additives such as sodium nitrate of the present invention when mixed with conventionally coated prills. In consequence, I have plotted in the drawing both the cube of the crater diameter for an equal weight of charge in each case, which gives an accurate measure of explosive effectiveness; and I have also plotted as a solid line in the drawing these same figures multiplied by the relative bulk density, which comes closer to being a practical measure of over-all explosive effectiveness for the reasons stated, when taking into account the cost of drilling holes.

Turning now to Table II and the drawing, it will be seen that small additions of sodium nitrate, including as much as 10% sodium nitrate in the mixture, decreases the efficiency of the ammonium nitrate when sensitized with diesel oil. Surprisingly, however, and completely in contrast to results obtained with other forms of ammonium nitrate, as already shown in Table I, when the uncoated ammonium nitrate prill is mixed with amounts of sodium nitrate from about 15% to about 75%, as is clearly evident from the drawing, then the explosive effectiveness is increased instead of being decreased, as one would normally expect. For percentages of sodium nitrate greater than about 75 the explosive efficiencies drop off to a very low value. Charges greater than 80% sodium nitrate did not give any crater at all and therefore are not plotted in the drawing.

While the results shown in Table II and in the drawing were obtained using Chile sodium nitrate, entirely comparable results are obtained with other forms of sodium nitrate, as appears from Table III which follows:

In the above table, uncoated ammonium nitrate prills were mixed with two difierent types of commercial sodium nitrate in a 70:30 ratio, and these mixtures were sensitized with diesel oil in three difierent concentrations, as shown in the table. in all cases, showing the virtual interchangeability of the sodium nitrates used, which is surprising in view of the significant difference in the particle sizes of the two forms of sodium nitrate whereas previous experimental workers with mixtures of sodium nitrate in explosives have found that particle size was of utmost importance, that is a very critical range must be maintained, neither too fine nor too coarse. This is not the case in my mixture. Another rather surprising efiect is that the liquid hydrocarbon used may be varied over a considerable range with no lessening of effectiveness. I have found that in general about 6 parts of hydrocarbon oil per 100 parts of the nitrate mixture works very well for all percentages of sodium nitrate within the inventive range, and this is the best concentration that I know of. This again is a somewhat surprising result, because the stoichiometrically equivalent amount of hydrocarbon oil increases greatly as the percentage of sodium nitrate increases, because of the great difference in oxygen balance of the two nitrates. The amount of diesel oil which I have found to be generally optimum, however, is not necessarily the stoichiometric quantity, but, as mentioned, simply about 6%.

The results of proceeding in accordance with the invention have been tested repeatedly by numerous experiments. Nevertheless, I am unable to offer any theory of action which would explain the surprising results obtained by the use of sodium nitrate with uncoated prilled ammonium nitrate. Possibly the mineral filler coating so commonly employed on prills has some dampening efiect, but that this is far from the entire explanation is Excellent results were obtained made clear by the fact that a 50-50 mixture of uncoated ammonium nitrate prills and potassium nitrate instead of sodium nitrate, together with 5.8 parts of diesel oil per 100 parts of nitrate mixture, fails to detonate at all. There is evidently something quite specific about sodium nitrate in my inventive compositions. Perhaps some interaction takes place at the crystal faces of the sodium nitrate and the ammonium nitrate, which one would expect to be inhibited by a normal filler coating. The explanation of the unusual results obtained with the inventive compositions must await intensive and fundamental research.

While the invention has been described with the aid of numerous specific examples, it will be evident from the disclosure that numerous variations of detail are permissible within the broad scope of the invention, keeping in mind, however, the experimental findings which I have set forth in the specification.

What I claim is:

l. A detonatable composition consisting essentially of uncoated prilled ammonium nitrate and sodium nitrate in a weight ratio within the range of 25% ammonium nitrate-% sodium nitrate and ammonium nitrate- 15% sodium nitrate, together with a liquid hydrocarbon in a Weight ratio of between 3 and 10 parts for each parts of the mixture of the said nitrates.

2. A detonatable composition consisting essentially of prilled ammonium nitrate, non-combustible coating thereon from 0% to not in excess of about /2 of the weight of said pulled ammonium nitrate and sodium nitrate in a weight ratio within the range of 25% ammonium nitram-75% sodium nitrate and 85 %-.ammonium nitrate- 15 sodium nitrate, together with a liquid hydrocarbon in a weight ratio of between 3 and 10 parts for each 100 parts of the mixture of the said nitrates.

3. The composition of claim 1 in which the liquid hydrocarbon is a petroleum hydrocarbon.

4. The composition of claim 2 in which the liquid hydrocarbon is a petroleum hydrocarbon.

5. A detonatable composition consisting essentially of uncoated prilled ammonium nitrate and sodium nitrate in a weight ratio within the range of 25% ammonium nitrate75% sodium nitrate and 85% ammonium nitrate- 15% sodium nitrate, together with about 6 parts diesel oil per 100 parts of mixed nitrates.

6. A detonatable composition consisting essentially of prilled ammonium nitrate, non-combustible coating thereon from 0% to not in excess of about /2 of the weight of said prilled ammonium nitrate and sodium nitrate in a weight ratio within the range of 25% ammonium nitrate-75% sodium nitrate and 85% ammonium nitrate- 15% sodium nitrate, together with about 6 parts diesel oil per 100 parts of mixed nitrates.

7. The composition of claim 1 in which the hydrocarbon is a petroleum hydrocarbon oil within the range of kerosene through light lubricating oil.

8. The composition of claim 2 in which the liquid hydrocarbon is a petroleum hydrocarbon oil within the range of kerosene through light lubricating oil.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A DETONATABLE COMPOSITION CONSISTING ESSENTIALLY OF UNCOATED PRILLED AMMONIUM NITRATE AND SODIUM NITRATE IN A WEIGHT RATIO WITHIN THE RANGE OF 25% AMMONIUM NITRATE-75% SODIUM NITRATE AND 85% AMMONIUM NITRATE 15% SODIUM NITRATE, TOGETHER WITH A LIQUID HYDROCARBON IN A WEIGHT RATIO OF BETWEEN 3 AND 10 PARTS FOR EACH 100 PARTS OF THE MIXTURE OF THE SAID NITRATES. 